The plot thickens... Shannon and Darren accuse Karstan of stealing after discovering missing timber in his unit following discovery of his secret room on The Block

A feisty Dee was throwing about accusations of cheating when the blockheads discovered Max and Karstan had been hiding a secret extra room that could potentially skyrocket the value of their apartment.

And the suspicions continued on Wednesday night's episode of The Block, when the more curious of the contestants took it upon themselves to find out if the sneaky couple had been hiding anything else.

Having noticed the supply of timber intended for their communal unit number six had dwindled significantly, a suspicious Shannon was quick to point the finger squarely at Karstan and enlisted the help equally distrusting Darren to get to the bottom of the mysterious disappearance.

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Snooping around: Shannon and Darren take it upon themselves to find out if Karstan has been hiding anything else on Wednesday's episode of The Block

Under watch: Karstan was suspected of stealing

'So it appears that the communal pile of timber in the hallway is smaller than what it should be and what it was yesterday so I'm thinking that someone's been taking a bit,' began Shannon.

'I've got a slight notion that Karstan might have taken it upstairs for his secret room - it's only a slight one but I wouldn't mind checking that out actually.'

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Piquing Darren's interest with the timber conundrum, the pair resolved on sneaking into Karstan's secret room for a good old-fashioned snoop around.

The two tradesmen trawled through the space digging around for any evidence to suggest their fellow contestant may have been thieving, but a quick survey proved fruitless.

Suspicious: After finding out that Karstan and Max have a hidden room, they think he may have stolen some communal timber to use in it

Mine! Shannon fails to find timber but discovers an extension lead of his

'There's nothing up here,' said Darren, somewhat disappointed to find the room wasn't stacked with piles upon piles of stolen goods.

'Except for my lead!' exclaimed Shannon in response, after he spotted his extension lead curled up in the framing of a wall.

'Look at that,' he said, pointing to a label that read 'MOS'.

Unsatisfied with their discoveries upstairs, Shannon and his partner-in-crime headed into Max and Karstan's unit where they stumbled across a much more interesting find - a couple of stray pieces of timber.

Curious: Unable to find anything upstairs they go into Karstan's unit searching for evidence of the theft

Ah ha! The pair stumble upon a pile of timber that looks suspiciously like the one missing

Not enough evidence: Keith is called in to inspect but he has his reservations

The accusatory couple resolve on calling foreman Keith to inspect the stockpile himself, but unconvinced he questions, 'What are you insinuating?'

'Put it this way, we ordered 50 sticks on your account for the study area yesterday,' said Darren.

'There are 21 sticks left and we haven't put any up...

'If this is your timber, why is it in here?' he offered, 'It's probably for [Karstan]'s secret room.'

Unaware: Karstan and Max had no idea the boys were snooping around their unit

Shaping up: The couple were outside doing a personal training session at the time

Working up a sweat: Max was forced to do lunges, sit ups and push ups as well as laps around the basketball court

Evaluating the information before him, Keith said: 'In all seriousness, each piece is about $50 so if someone's going to steal 20 links, that's a grand.'

While the evidence looked convincing enough to incriminate Karstan, a level-headed Keith noted that the timber could be old and that they couldn't go pointing any fingers until every avenue had been looked into.

Max and Karstan were unaware of all the drama going on in their apartment and had escaped the block for the morning to squeeze in a quick personal training session.

While the loved-up duo were out bulking up, Simon was looking more gaunt than ever as he worked tirelessly through the night.

The pressure of the competition's tight deadlines and endless hours certainly took a toll on the 28-year-old who lost seven kilos while filming the show.

Too thin: Simon was looking thinner than ever after working tirelessly on his unit

Very tired: His face looked very gaunt and he complained of feeling fatigued

Shocking: Simon lost a total of seven kilos while working on The Block